The nature of samsaric evolution is not such that death is followed by nothingness, nor that humans are always reborn as humans and insects as insects. On the contrary, we all carry within us the karmic potencies of all realms of cyclic existence. Many beings transmigrate from higher to lower realms, others from lower to higher. The selection of a place of rebirth is not directly in our own hands but is conditioned by our karma and delusions. They who possess spiritual understanding can control their destiny at the time of death, but for ordinary beings the process is very much an automatic chain reaction of karmic seeds and habitual psychic response patterns....
Our repeated experience of frustration, dissatisfaction and misery does not have external conditions as its root cause. The problem is mainly our lack of spiritual development. As a result of this handicap, the mind is controlled principally by afflicted emotions and illusions. Attachment, aversion and ignorance rather than a free spirit, love and wisdom are the guiding forces. Recognizing this simple truth is the beginning of the spiritual path.
~ by H.H. the Dalai Lama, translated and edited by Glenn Mullin, from The Path to Enlightenment, published by Snow Lion Publications